Mu-lac insertion mutants of E. coli with altered expression in the presence of salicyl alcohol or that fail to exhibit altered antibiotic sensitivity when exposed to salicyl alcohol have been isolated. Five antibiotic-sensitive mutants were selected on the basis that their resistance to nalidixic acid increased only minimally when grown in the presence of salicyl alcohol. Two of these mutants were also hyper- sensitive to nalidixic acid in the presence of sodium salicylate. The failure of salicyl alcohol or salicylates to induce antibiotic resistance was drug-specific in four of the five mutants. In one, however, salicyl alcohol failed to induce resistance to ampicillin as well as to nalidixic acid. This mutant responded normally to both antibiotics when grown in sodium salicylate. The mutants have been roughly mapped by Hfr crosses and are currently being sequenced. Over 100 mutants that fail to express beta-galactosidase in the presence of salicyl alcohol have been isolated and are being examined. Preliminary data suggests that the genes mutated in this class are principally expressed in mid-log phase and not in early log phase or at saturation density. We are tentatively referring to these genes as mid- life crisis genes. No mutant was found that increased the expression of beta-galactosidase in the presence of salicyl alcohol.